Optimization of free space optics parameters: An optimum solution for bad weather conditions

Abstract

Free Space Optics Systems (FSO) is one of the most effective solutions, especially for atmospheric turbulence due to the weather and environment structure. Free space optics system suffers from various limitations. A well-known disadvantage of FSO is its sensitivity on local weather conditions-primarily to haze and rain, resulting in substantial loss of optical signal power over the communication path. The main objective of this article is to evaluate the quality of data transmission using Wavelength Division Multiplexing (WDM) with highlighting several factors that will affect the quality of data transmission. The results of these analyses are to develop a system of quality-free space optics for a high data rate transmission. From the result analysis, FSO wavelength with 1550 nm produces less effect in atmospheric attenuation. Short link range between the transmitter and receiver can optimize the FSO system transmission parameters or components. Based on the analysis, it is recommended to develop an FSO system of 2.5 Gbps with 1550 nm wavelength and link range up to 150 km at the clear weather condition of bit-error-rate (BER) 10⁻⁹.

Introduction

Free space optics based on WDM system suffers from various limitations, especially atmospheric turbulence due to the weather and environment structure [1], [2]. Atmospheric attenuation of FSO system is typically dominated by haze and fog, but is also dependent upon rain and dust. The total attenuation is a combination of atmospheric attenuation and geometric losses. Scattering produced by atmospheric particles can be considered as a form of dispersion of the energy that makes the signal divert from its original target. Geometrical scattering is the result of raindrops and snow that are made of larger molecules having an impact similar to Raleigh scattering. Turbulence is the random fluctuation in the refraction index of air produced by differential heating and has the effect of defocusing the beam, producing intensity fluctuations in the received signal (scintillation), and contributing to the spreading of the transmitted beam. Turbulence is partially compensated by tracking and adaptive optics techniques, and it has a greater impact on higher frequencies within the near infrared sub-band (1550 nm is therefore, less affected) [7]. In other words, weather, link distance, scattering, absorption, turbulence, misaiming, laser wavelength, and data rates all have an impact and must be factored into either a custom calculated link budget or a manufacturer's distance rating [3]. Fiber optics continues to be deployed at a measured and sustained pace, but the cost to do so is often prohibitive, the process long, and the investment irreversible. Conversely, optical wireless solutions complement fiber optics in networks with considerably less expense, faster deployment, and flexible service rollouts, including same-day connectivity, due to their ease of installation and maintenance [4]. Implementing optical data links through the atmosphere over long distance and high data rate is challenging due to beam degradation cause by atmospheric turbulence [4], [5]. To avoid this limitation various way of designing free space optic based on WDM systems are needed. In this article, a new approach is proposed to overcome the above mentioned limitations. The proposed system is based on optimization the main FSO parameters in order to increase the overall system performance. The remainder of this article is divided as follows: Section 2, analysis the characteristic and expression of free space optic attenuation that involves under Malaysia's weather condition. In Section 3, Simulation Results have been presented. Section 4, optimizes the parameters of the WDM system based on FSO that improved the system performance in terms of quality of the transmission. Finally, conclusion is reported in Section 5.